1. Field Of The Invention
This invention relates generally to tunable circuits and more particularly to miniature dynamically tunable circuits of a type that can be fabricated on integrated circuit substrates.
2. Description Of The Related Art
With integrated circuit technology, size and space are a serious constraint on circuit designers. For example, very small dimensioned, thin film circuit elements are fabricated directly onto the surface of a dielectric substrate. Very often these individual circuit elements have different characteristic impedances than the circuit elements to which they are coupled. Since it has been difficult to utilize variable tuners for impedance matching because of the small dimensions involved and the density of circuit elements, such lines have typically been tuned to a fixed impedance match.
Unfortunately, the circuit element impedances change with normal variations in the processed integrated circuit.
Consequently, the impedance match can be lost. As a result of the fixed nature of the circuit element tuning, the resulting operating flexibility and performance of the overall integrated circuit is undesirably affected.
These challenges have often been met by the use of active semiconductor devices for circuit tuning purposes. The use of active semiconductor devices for such tuning is described by I. Bahl and P. Bhartia in Microwave Solid-State Circuit Design, John Wiley & Sons (1988), pages 373 through 422. While these types of devices are characterized by their small sizes, they do present other challenges to the circuit designer. For example, they typically introduce significant losses and have limited ranges and power handling capabilities.
With the advent of micro-machining it has been shown that it is feasible to fabricate miniature mechanical and electro-mechanical devices using thin film integrated circuit technology. Some specific examples are the levers, gears, sliders, and springs referred to in U.S. Pat. No. 4,740,410, issued on Apr. 26, 1988, to R. S. Muller et al., and entitled Micro Mechanical Elements and Methods for Their Fabrication. In addition, electro-mechanical devices such as rotatable motors and linear motors are described in U.S. Pat. No. 4,754,185, issued on Jun. 28, 1988 to K. J. Gabriel et al., and entitled Micro-Electrostatic Motor.